[Illustration: FIG. 74. _Proechimys guyannensis nesiotes_, male, CNHM no. 19496, Ilha de Manapirí. Type. × 1.] [Illustration: FIG. 75. _Proechimys guyannensis leioprimna_, female, CNHM no. 19503, Cametá. Type. × 1.] [Illustration: FIG. 76. _Proechimys guyannensis oris_, male, CNHM no. 19495, Providencia. × 1.] [Illustration: FIG. 77. _Proechimys guyannensis arescens_, male, CNHM no. 26440, Fazenda Inhuma. Paratype. × 1.] [Illustration: FIG. 78. _Proechimys guyannensis riparum_, female, AMNH no. 143018, Manaus. Type. × 1.] [Illustration: FIG. 79. _Proechimys guyannensis arabupu_, male, AMNH no. 75816, Arabupu. Type. × 1.] [Illustration: FIGS. 80, 81. _Proechimys guyannensis villicauda_, male, MN no. 1932, Tapirapoã. Type. × 1.] [Illustration: FIGS. 82, 83. _Proechimys guyannensis ribeiroi_, male, MN no. 1935, Rio Doze de Outubro. Type. × 1.] [Illustration: FIGS. 84, 85. _Proechimys guyannensis hyleae_, male, MCZ no. 30887, Tauarí. Type. × 1.] [Illustration: FIGS. 86, 87. _Proechimys guyannensis nesiotes_, male, CNHM no. 19496, Ilha de Manapirí. Type. × 1.] [Illustration: FIGS. 88, 89. _Proechimys guyannensis leioprimna_, female, CNHM no. 19503. Type. × 1.] [Illustration: FIGS. 90, 91. _Proechimys guyannensis oris_, male, CNHM no. 19495, Providencia. × 1.] [Illustration: FIGS. 92, 93. _Proechimys guyannensis arescens_, male, CNHM no. 26440, Fazenda Inhuma. Paratype. × 1.] [Illustration: FIGS. 94, 95. _Proechimys guyannensis riparum_, female, AMNH no. 143018, Manaus. Type. × 1.] [Illustration: FIGS. 96, 97. _Proechimys guyannensis arabupu_, male, AMNH no. 75816, Arabupu. Type. × 1.] =Proechimys guyannensis ribeiroi= subspecies nova _Type locality._--Rio 12 de Outubro, affluent of the Camararé, _Mato Grosso_, Mato Grosso, Brazil; about 190 kilometers west of Utiarití; altitude 414 meters. _Type_: Museu Nacional, no. 1935, adult male (colors faded); collected on 20 June, 1909, by Prof. A. Miranda Ribeiro; original number _G._ _Range._--Known only from the type locality. _Diagnosis._--_Aristiforms wide and stiff_; incisive foramen small and narrow; vomerine sheath complete and thick; p4 with four counterfolds; remaining molariform teeth with three counterfolds. _Pelage._--_Aristiforms on middorsal region_: Whitish basally, gradually blackening toward tip; total length, 19 to 22 mm; maximum width, 0.8 mm. _Setiforms on middorsal region_: Whitish on basal half, gradually blackening toward tip but interrupted by subapical zone probably of some tint of ochraceous; total length, 22 to 24 mm; maximum width, 0.06 mm. _Setiforms on outer thighs_: Whitish basally, gradually blackening toward tip but interrupted by probably light ochraceous, subapical zone; total length 14 to 16 mm; maximum width, 0.03 mm.